Crystallization kinetics and melting of caprolactone random copolymers

Spherulitic growth rates and overall rates of crystallization of poly(ε‐caprolactone‐co‐ε‐methyl‐ε‐caprolactone), poly(CL‐co‐MCL), were analyzed over a composition range from pure poly (ε‐caprolactone) (PCL) to a copolymer containing 40% MCL with an equation which contains the classical nucleation and transport terms, but adds an entropic factor to the nucleation term. Using this new equation, linear plots were obtained with slopes corresponding to the value of the nucleation parameter ( K G 2 ) The experimental K G 2 value, (9.6 ± 0.5) × 10 4 K 2 , is independent of the comonomer content; also, the same K G 2 value is obtained from measurements of the overall rate of crystallization and from growth rate analysis. The interfacial free energy (σ e ) is 112 ± 5 erg/cm 2 . The melting behavior of PCL and poly(CL‐co‐MCL) is also reported. Equilibrium melting temperatures were determined by the Hoffman‐Weeks extrapolation method. It was found, using the melting point depression method, that 71% of the MCL units are incorporated into the PCL crystals at equilibrium. According to the Z criterion proposed by Lauritzen, Regime II applies to the crystallization kinetics of all polymers investigated. Finally, the value of the Avrami parameter n is reported.